The process of signal transduction and the genetic relationship of the genes involved as well as their targets have been intensely studied and we are beginning to get a clear idea of how these signals specify cell fates and direct development. Still poorly understood is the mechanism by which signals are translated into the activation and/or repression of downstream target genes. Studies on pattern formation in the leg of Drosophila have focused on two major signaling pathways that create a distalizing gradient in the formation of the Proximo-Distal (PD) axis. The current model suggests that this gradient is differentially read out by at least three target genes along the PD axis. This model is supported by genetic and molecular studies; however the mechanism by which this gradient is read remains unknown. The focus of this proposal is to test the hypothesis that these signals are in fact directly read out by the target genes and done so in a graded fashion. The approach taken will involve the isolation and dissection of cis-regulatory elements that drive expression of reporter genes in response to the gradient. These elements will be tested through targeted mutagenesis and binding assays to determine the factors responsible for transcriptional activation. [unreadable] [unreadable] [unreadable]